The present invention relates to a bi-level image processing method and apparatus such as a method and apparatus for converting the resolution of a bi-level image, or for compressively encoding a bi-level image.
Although a bi-level image comprises only black and white dots, many bi-level images exploit the integrating capability of the human visual system to express different levels of gray by means of patterns in which black dots appear with different densities. These patterns are generated by linear interpolation and other well-known techniques, and the arrangement of black dots in the patterns is essentially random.
Random arrangements create problems in various types of image processing. As one of these problems, when the resolution of a bi-level image is converted, random arrangements of black dots tend to generate unwanted patterns, referred to as texture, in the converted image. As another problem, when the image is compressively encoded, the randomness of the dot patterns prevents high compression ratios from being attained.